The present invention relates to an electronic control unit that is able to transmit vehicle identifying information on demand from an external scan tool connected to a communication line, and a vehicular electronic control system having a plurality of the electronic control units.
It has been proposed that a vehicular electronic control system having electronic control units (ECUs) provided for different components of a vehicle, respectively, in the manner that they communicate each other. A diagnostic system installed on a vehicle having such a system is required to be compliant with an on-board diagnostic system II (OBD-II). When an external scan tool (tester) is connected to each ECU included in the vehicle at a repair shop, a vehicle identifying number (VIN) code can be read in a predetermined communication format, such as a KWP diagnostic communication format. The VIN code is uniquely assigned to each vehicle. With the VIN code, a mechanic at the repair shop can obtain various kinds of information on the vehicle and provide appropriate repair work on the vehicle.
In such a system, if multiple ECUs simultaneously send responses to a VIN code transmission request issued by the scan tool, data collisions frequently occur on a communication line. As a result, the usability of the communication line reduces and loads on the ECUs increase. This problem will become more serious as more ECUs are connected to the communication line.
Moreover, a recently revised OBD-II regulation requires that the number of VIN codes transmitted from one vehicle must be one. To meet this requirement, only one ECU may be configured to transmit the VIN code to the scan tool. In this case, the VIN code cannot be transmitted if the ECU becomes defective or a communication line connected to the ECU is broken. To solve this problem, all onboard ECUs may be configured to transmit the VIN code to the scan tool. However, all ECUs simultaneously transmit the VIN code. This does not meet the requirement of the revised OBD-II.
The present invention therefore has an objective to provide a vehicular electronic control system having multiple ECUs in which vehicle identifying information is efficiently transmitted from one of the control units. A vehicular electronic control system of the present invention includes multiple ECUs and configured to transmit the vehicle identifying information responding to a request issued by an external scan tool that is connected to a communication line. The ECUs are intercommunicative via the communication line.
Each ECU includes a storing means, a detecting means, a timing means, and a communication means. The storing means stores the vehicle identifying information, that is, a VIN code. The detecting means monitors the communication line and detects an output indicative the VIN code sent from another ECU to the scan tool. The timing means times an elapsed time since the ECU has received the VIN code transmission request issued by the scan tool. The timing means of each ECU times an response start time preset for the ECU based on its priority level. When the time has elapsed, the communication means transmits the VIN code stored by the storing means to the scan tool if the detecting means has not detected the output from another ECU.
With this configuration, when the ECU having the highest priority, that is, having the earliest response start time, is unable to transmit the VIN code, the ECU having the next highest priority transmits the VIN code. The ECUs transmit the VIN code in order of precedence when the ECU having higher priority is unable to transmit the VIN code when another ECU has not transmitted the VIN code. Therefore, the VIN code is never transmitted from multiple ECUs.
Furthermore, collisions of data transmitted from multiple ECUs on the communication line are less likely to occur. As a result, high usability of the communication line is provided. While one of the ECUs is transmitting the VIN code, the communication means of other ECUs are not in operation. Therefore, loads on the ECUs are effectively reduced, especially when the system has a large number of ECUs.
Still further, other ECUs do not transmit the VIN code when one of the ECUs has transmitted the VIN code. Thus, the system can satisfy the revised OBD-II requirement.